[Andreas]

PHP Code:

$thread = $DB_site->query_first("SELECT thread.*,post.* FROM " . TABLE_PREFIX . "thread AS thread
                                 LEFT JOIN " . TABLE_PREFIX . "post AS post ON (post.postid=thread.firstpostid)
                                 WHERE thread.threadid=$threadid"); 


Instead of thread.*,post.* you can restrict it to the fields you really need.
So if you only want Author, Title, Date and Text this would be

thread.postusername, tread.title, thread.dateline, post.pagetext